Method and System for Purifying Liquified Gases

ABSTRACT

A method system for providing a purified liquified gas including a vessel containing adsorbent submerged within a liquified gas and an impurity contained inside a storage tank wherein the liquified gas is purified by the adsorbent.

CROSS-REFERENCE TO RELATED APPLICATIONS

None

BACKGROUND

Liquified gases that are normally stored, or initially produced, in theliquid state at low or very low temperatures often need to be purifiedto an acceptable level of purity associated with their end use. It wouldbe advantageous if they could be purified easily and economically. Theterm, liquified gas, is defined as a substance in a liquid state thatotherwise predominantly exist as a gas if it is maintained at oneatmosphere and 15° C. A few specific examples of such include Nitrogen,Oxygen, Helium, Neon, Argon, Krypton Xenon, Hydrogen, Methane, andCarbon Dioxide.

SUMMARY

A first method is disclosed for providing a purified liquified gas thatincludes the following steps:

-   -   at least one vessel is provided containing adsorbent submerged        within a liquified gas and at least one impurity that are        contained inside a storage tank;    -   the liquified gas is allowed to flow into the at least one        vessel containing adsorbent thereby purifying the liquified gas        by preferentially adsorbing the at least one impurity on the        adsorbent in comparison to the liquified gas; and    -   the purified liquified gas is allowed to flow out of the at        least one vessel and out of the storage tank and into a conduit        for directing the purified liquified gas to another storage        tank, a point of use or a vaporizer.

A second method is disclosed for providing a purified liquified gasincluding the following steps:

-   -   first and second vessels are provided each containing an        adsorbent, each of the first and second vessels being submerged        within a liquified gas and at least one impurity that are        contained inside a storage tank;    -   the liquified gas is allowed to flow out of the storage tank,        back into the storage tank and into the first vessel thereby        purifying the liquified gas by preferentially adsorbing the at        least one impurity on the adsorbent in comparison to the        liquified gas;    -   the purified liquified gas is allowed to flow out of the first        vessel and out of the storage tank and into a conduit for        directing the purified liquified gas to another storage tank, a        point of use or a vaporizer; and    -   the adsorbent contained in the second vessel is regenerated,        thereby desorbing at least some of the at least one impurity,        wherein the regeneration is performed concurrently with the step        of allowing the liquified gas to flow out of the storage tank.

A system is disclosed for providing a purified liquified gas thatincludes the following elements:

-   -   a storage tank containing a liquified gas and at least one        impurity;    -   at least one vessel containing adsorbent submerged within the        liquified gas and the at least one impurity, the adsorbent        having the property of preferentially adsorbing the at least one        impurity in comparison to the liquified gas; and    -   a conduit in fluid communication with said at least one vessel        configured and adapted to direct liquified gas purified by said        at least one vessel to a point of use, a different storage tank,        or a vaporizer.

The first method or second method or system can also include one or moreof the following aspects:

-   -   the liquified gas is liquid Nitrogen.    -   the liquified gas is liquid Oxygen    -   the liquified gas is liquid Helium    -   the liquified gas is liquid Argon    -   the liquified gas is liquid Hydrogen    -   the liquified gas is liquid Carbon Dioxide    -   the at least one vessel containing adsorbent includes first and        second vessels containing adsorbent and:        -   concentration of the at least one impurity of purified            liquified gas exiting the first vessel is monitored    -   the flow of liquified gas into the first vessel is discontinued        and        -   the adsorbent contained in the first vessel is regenerated    -   the adsorbent contained in the at least one vessel is        regenerated by purging it with an inert gas and allowing the        purge gas to be vented from the at least one vessel and storage        tank (wherein optionally the purge gas is the same as the        purified liquified gas)    -   the adsorbent contained in the at least one vessel is        regenerated by allowing a temperature of the at least one vessel        to rise thereby desorbing the at least one impurity and allowing        the at least one impurity to be vented from the at least one        vessel and storage tank, wherein optionally        -   the temperature of the at least one vessel is allowed to            rise by heating the at least one vessel with an electric            heater associated with the vessel, or        -   the temperature of the at least one vessel is allowed to            rise by purging the at least one vessel with a heated purge            gas, or        -   the temperature of the at least one vessel is allowed to            rise by passing a heated heat exchange fluid through heat            exchangers located inside the at least one vessel    -   the storage tank is allowed to empty itself of liquified gas and        be vented thereby raising a temperature of the at least one        vessel and the at least one vessel is vented thereby desorbing        the impurity    -   the liquified gas is liquid Helium and the purge gas is Nitrogen        or Argon    -   at least one impurity comprises an impurity that predominantly        exists as a gas if it is maintained at one atmosphere and 15° C.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawing, andwherein:

The Figure is a schematic of a particular embodiment of the disclosure.

DESCRIPTION OF PREFERRED EMBODIMENTS

This invention concerns the purification of liquified gases that arenormally stored, or initially produced, in the liquid state at low orvery low temperatures. The purification apparatus that can be used toremove dissolved or entrained impurities within the initially produced(and nearly pure) liquified gas includes one or more vessels containinga suitable pre-activated adsorbent material such as a molecular sieve,activated carbon, silica gel, activated alumina, or an inert materialimpregnated with metals or metal alloys (such as Pd/Al2O3 or Hopcalite),and the like.

The vessel containing adsorbent is submerged within the liquified gas tobe purified contained in a storage tank. Thus, cooling of the vessel maybe achieved by direct contact with the liquified gas to be purified orby exchanging heat between the liquified gas and the vessel via a heatexchange fluid. Optionally, the vessel may be vacuum-jacketed.Preferably, the vessel will be installed near or at the bottom of thestorage tank in which they are to be used.

The purification process involves passing the liquified gas through atleast one (the first) vessel containing adsorbent and then allowing thepurified liquified gas to exit the vessel and then exit the storage tankinto a piping system leading to either a different storage tank,conventional external vaporizers (if the gas phase of the purifiedliquid must be produced) or to a point of use if it is to be useddirectly in the liquid state. Following the external vaporizationprocess, the purified gas may be directed through an appropriate pipingnetwork to a point of use location.

The vessel may have filters at one or both ends to providepre-filtration of solid particles entrained in the liquified gas and/orpost-filtration of solid particles in the purified liquified gas thatmay be caused by dislodgement of the adsorbent.

External low temperature or cryogenic valves (either manuallyautomatically controlled) attached by an appropriate piping network canbe used to control the flow of the liquified gas to be purified throughthe vessel or to bypass the vessel, if necessary, or to redirect theflow of liquified gas through additional vessels containing adsorbent.

Conventional analytical techniques can be used to monitor theconcentration of impurities within the purified liquified gas in orderto monitor the performance of a particular adsorbent vessel in currentuse. If and when a selected impurity breakthrough occurs, the liquifiedgas to be purified can be directed (either manually or automatically)into a second vessel containing adsorbent and the purification processcan be resumed as noted above.

Regeneration of the vessel can be achieved without heating by allowingthe entire empty bulk storage tank (as well as the vessel) to warm up toambient temperatures while, at the same time, venting the vaporizedcontents of the vessel to the ambient atmosphere. This process willallow the desorption of practically all adsorbed impurities trappedwithin the adsorbent.

Alternatively, a more rapid and complete regeneration process can beachieved by passing an ambient temperature (or heated) flow of a purgegas through a vessel containing spent adsorbent. The purge gas can be agaseous form of the same liquified gas initially purified or it may beanother less expensive gas. For example, if liquid Helium had beeninitially purified in this way, a cheaper purge gas (such as Nitrogen orArgon) might be used during the purging/regeneration process since thesegases are much less expensive than relatively pure Helium. All of theabove noted manipulations can be preformed manually or automaticallythrough externally located manual or automatic valves.

In addition to the above noted operation, the vessel containingadsorbent may be designed to contain a vacuum jacketed covering thatwould facilitate the installation of an electrical heating system insidethe vessel so it could be regenerated by internal heating as well asusing an external flow of some type of purge gas during the heatingprocess. This kind of regeneration process could be executed even if thebulk fluid storage tank was not empty.

A further improvement associated with this purification process is thatit allows for the purification of very cold liquified gases even if theyexist at temperatures well above their normal boiling points and wellabove 1.0 atmosphere in pressure while still existing in the liquidstate within a suitable high pressure storage tank. Two typical examplesof these kinds of fluids are liquid Nitrogen and liquid Oxygen storedwithin conventional high-pressure bulk cryogenic storage tanks.

In the case of standard bulk liquid Nitrogen storage tanks, the ullagepressure may typically be deliberately set at about 90 psig (lowpressure source) to about 160 psig (high pressure source), depending ona particular user's requirements. These pressures may be achieved withinthe bulk liquid storage tanks by allowing the liquid Nitrogen to reachtemperatures that maintain a preset value for the stored liquid'stemperature. These temperatures may be reached via ambient temperatureheat leaks through the storage tank walls into the fluid to be purifiedor by using some other type of active heat exchanger well known to thoseskilled in the art, for example, a pressure building coil locatedoutside of the bulk fluid storage tank.

In the case of liquid Nitrogen at 90 and 160 psig, the temperatures thatare associated with these liquid vapor pressures are about 99° K and106° K, respectively. These temperatures are still very cold but theyare also about 22° K and 29° K, respectively, hotter than the normalboiling point of liquid Nitrogen which is about 77° K (at 1.0 atmosphereabsolute).

A typical storage tank pressure for bulk liquid oxygen is about 120psig. At this pressure, the temperature of the self-pressurized liquidOxygen is about 118° K. So, under these conditions, the liquid Oxygen isstill very cold, but it is also about 28° K hotter than the normalboiling point of 90.2° K (at 1.0 atmosphere absolute) for liquid Oxygen.

Legend to the Figure:

1) storage vessel

2) pressurized, low temperature fluid to be purified

3) relief valve

4) adsorbent filled vessel

5) adsorbent filled vessel

6) adsorbent filled vessel

7) conduit

8) relief valve

9) fluid flow control valve to vaporizers

10) conduit

11) fluid control valve to conduit 7

12) fluid flow control valve to adsorbent filled vessel 4

13) fluid flow control valve to adsorbent filled vessel 5

14) conduit

15) conduit

16) conduit

17) conduit

18) conduit

24) fluid flow control valve to adsorbent filled vessel 6

As shown in the Figure, one particular embodiment includes threeseparate adsorbent vessels 4, 5, 6 installed inside of a conventionalbulk storage tank 1 containing a liquified gas 2. During purification,liquified gas 2 exits the tank 1 via conduit 10. Valve 11 is closedthereby preventing delivery of the liquified gas without first beingpurified by the adsorbent filled vessels 4, 5, 6. One or more of valves12, 13, 24 are open thereby allowing liquified gas 2 to flow intoadsorbent filled vessels 4, 5, 6, respectively, via conduit 18. Much ofthe entrained or dissolved impurities in the liquified gas 2 is adsorbedby vessels 4, 5, 6. The thus-purified liquified gas 2 exits theadsorbent filled vessels 4, 5, 6 and enters conduit 7 via conduits 14,15, 16, respectively. Valve 9 controls the flow of purified fluid 2 inconduit 7 to either external vaporizers (not shown), a different storagetank (not shown) or a point of use (not shown).

If for some reason, purification via the adsorbent filled vessels 4, 5,6 is not desired but a flow of liquified gas 2 to the externalvaporizers, different storage tank, or point of use is desired, valves12, 13, 24 are closed and valve 11 is opened allowing the fluid 2 todirectly enter conduit 7. Also, as apparent to one of ordinary skill inthe art, one or more of the adsorbent filled vessels 4, 5, 6 may beisolated via manipulation of valves 12, 13, 24 thereby preventingpurification of the fluid 2 by that adsorbent filled vessel or vessels4, 5, 6. In this manner, purification of the liquified gas 2 may occurinside one or two of the vessels 4, 5, 6, while the adsorbent in two orone of the vessels 4, 5, 6 is regenerated.

All external piping lines (except for piping networks that aredownstream of external vaporizers) are preferably vacuum insulated (orotherwise insulated) if used to convey low temperature fluids.

Additional valves may be used to direct selected external sources of apurge gas through the adsorbent filled vessels 4, 5, 6. In such case,one typical location is between valve 11 and valves 12, 13, 24. Ventingvalves may also be located between valve 9 and relief valve 8 tofacilitate the regeneration process. Finally, pressure relief valves 3,8 may be activated in case of too great a pressure is reached.

Preferred processes and apparatus for practicing the present inventionhave been described. It will be understood and readily apparent to theskilled artisan that many changes and modifications may be made to theabove-described embodiments without departing from the spirit and thescope of the present invention. The foregoing is illustrative only andthat other embodiments of the integrated processes and apparatus may beemployed without departing from the true scope of the invention definedin the following claims.

1. A method for providing a purified liquified gas, comprising the stepsof: providing at least one vessel containing adsorbent submerged withina liquified gas and at least one impurity that are contained inside astorage tank; allowing the liquified gas to flow into the at least onevessel containing adsorbent thereby purifying the liquified gas bypreferentially adsorbing the at least one impurity on the adsorbent incomparison to the liquified gas; and allowing the purified liquified gasto flow out of the at least one vessel and out of the storage tank andinto a conduit for directing the purified liquified gas to anotherstorage tank, a point of use or a vaporizer.
 2. The method of claim 1,wherein the liquified gas is liquid Nitrogen.
 3. The method of claim 1,wherein the liquified gas is liquid Oxygen.
 4. The method of claim 1,wherein the liquified gas is liquid Helium.
 5. The method of claim 1,wherein the liquified gas is liquid Argon.
 6. The method of claim 1,wherein the liquified gas is liquid Hydrogen.
 7. The method of claim 1,wherein the liquified gas is liquid Carbon Dioxide.
 8. The method ofclaim 1, wherein the at least one vessel containing adsorbent comprisesfirst and second vessels containing adsorbent, said method comprisingthe further steps of: monitoring a concentration of the at least oneimpurity of purified liquified gas exiting the first vessel;discontinuing the flow of liquified gas into the first vessel; andregenerating the adsorbent contained in the first vessel.
 9. The methodof claim 1, further comprising the step of regenerating the adsorbentcontained in the at least one vessel by purging it with an inert gas andallowing the purge gas to be vented from the at least one vessel andstorage tank.
 10. The method of claim 1, further comprising the step ofregenerating the adsorbent contained in the at least one vessel byallowing a temperature of the at least one vessel to rise therebydesorbing the at least one impurity and allowing the at least oneimpurity to be vented from the at least one vessel and storage tank. 11.The method of claim 10, wherein the temperature of the at least onevessel is allowed to rise by heating the at least one vessel with anelectric heater associated with the vessel.
 12. The method of claim 10,wherein the temperature of the at least one vessel is allowed to rise bypurging the at least one vessel with a heated purge gas.
 13. The methodof claim 1, comprising the steps of: allowing the storage tank to emptyitself of liquified gas and be vented thereby raising a temperature ofthe at least one vessel; and venting the at least one vessel therebydesorbing the impurity.
 14. The method of claim 9, wherein the purge gasis the same as the purified liquified gas.
 15. The method of claim 9,wherein the liquified gas is liquid Helium and the purge gas is Nitrogenor Argon.
 16. The method of claim 10, wherein the temperature of the atleast one vessel is allowed to rise by passing a heated heat exchangefluid through heat exchangers located inside the at least one vessel.17. The method of claim 1, further comprising the steps of: allowing thestorage tank to empty itself of liquified gas and be vented therebyraising a temperature of the at least one vessel; purging the at leastone vessel with a purge gas; and allowing the purge gas to be ventedfrom the at least one vessel.
 18. The method of claim 1, furthercomprising the step of allowing the liquified gas to flow out of thestorage tank and back into the storage tank before said step of allowingthe liquified gas to flow into the at least one vessel containingadsorbent.
 19. A method for providing a purified liquified gas,comprising the steps of: providing first and second vessels eachcontaining an adsorbent, each of the first and second vessels beingsubmerged within a liquified gas and at least one impurity that arecontained inside a storage tank; allowing the liquified gas to flow outof the storage tank, back into the storage tank and into the firstvessel thereby purifying the liquified gas by preferentially adsorbingthe at least one impurity on the adsorbent in comparison to theliquified gas; allowing the purified liquified gas to flow out of thefirst vessel and out of the storage tank and into a conduit fordirecting the purified liquified gas to another storage tank, a point ofuse or a vaporizer; and regenerating the adsorbent contained in thesecond vessel thereby desorbing at least some of the at least oneimpurity, wherein said step of regenerating is performed concurrentlywith said step of allowing the liquified gas to flow out of the storagetank.
 20. A system for providing a purified liquified gas, comprising: astorage tank containing a liquified gas and at least one impurity; atleast one vessel containing adsorbent submerged within the liquified gasand the at least one impurity, the adsorbent having the property ofpreferentially adsorbing the at least one impurity in comparison to theliquified gas; and a conduit in fluid communication with said at leastone vessel configured and adapted to direct liquified gas purified bysaid at least one vessel to a point of use, a different storage tank, ora vaporizer.
 21. The system of claim 20, wherein the liquified gas isliquid Nitrogen.
 22. The system of claim 20, wherein the liquified gasis liquid Oxygen.
 23. The system of claim 20, wherein the liquified gasis liquid Helium.
 24. The system of claim 20, wherein the liquified gasis liquid Hydrogen.
 25. The system of claim 20, wherein the liquifiedgas is liquid Carbon Dioxide.
 26. The system of claim 20, furthercomprising: a source of purge gas; and a conduit in fluid communicationbetween the source of purge gas and the at least one vessel.
 27. Thesystem of claim 20, wherein the at least one vessel containing adsorbentcomprises first and second vessels each containing adsorbent.
 28. Thesystem of claim 20, further comprising: a source of purge gas; and aconduit in fluid communication between the source of purge gas and theat least one vessel.